A joystick is a device shaped like a stick that people use to interact with video games.

There are many different kinds of joysticks. Joysticks on their own are pretty phallic, but a couple of the new ones out there actually look a lot like real penises.

Arcade joysticks:
Short, with a plastic ball on top. Pretty standard on most arcade machines. The hand usually cups over the top, but some use the underhand joystick grip. These sticks are usually used with one hand, while [double finger hand.
The NES Advantage copied this design for use on the NES. Very nice.

Old joysticks:
These joysticks usually had one or two buttons, one the top or head of the stick and/or one on the base of the joystick, usually to the top-left. Both buttons were for thumb use.

On the Commodore 64, many one-player games set the joystick at Port 2 instead of the more logical Port 1. I assume this was because Port 2 was easier to implement.

See also:
Atari-joystick / TAC-2

New joysticks:
Tonnes of buttons. I've never actually used one of these. See also:
Microsoft Sidewinder

Joystick ascii interpretation:
       _         ||
 m1a  |-|        ||
  ____| |____    ||
 /   _| |_   \   ||
|  / ,| |. \  |  //
| ( ( '-' ) ) |_//
|  \ `'"'' /  |-'
|   `-----'   ;
|\___________/| 
|             ; 
 \___________/
Other video game interactors include:
keyboard
koala pad
gamepad/d-pad
light gun
light pen
mouse
paddle
Power Glove